Preheat oven to 180 degrees. Prepare a muffin tray, or a springform pan (depending if you want lots of little tarts (we did) or one big one).Crush biscuits. Melt the butter. Combine in a mixing bowl.Line the bottom and the sides of the muffin cases/springform pan with the biscuit crumbs.Bake the cases in the oven for 10 minutes - the house should start to smell like chocolate biscuits.Pull the cases out and leave to cool on a wire rack (keep them in the tray/pan).Meanwhile, whisk together eggs, yolk, sugar, cream, vanilla and salt in a large bowl.Melt the chocolate and add the butter, stirring until combined, and mixture is smooth and glossy.Let the chocolate cool (if its too hot, it will cook the eggs).Then add it to the egg/cream mix and whisk gently until combined (over-whisking will produce airbubbles...not good).Pour the chocolate filling into the prepared crusts, and then place in the oven for 22-28 minutes (longer = firmer, shorter = gooey)Cool on a wire rack.

Serve warm with a dusting of cocoa powder and icecream or cold with raspberries and whipped cream.

TipsAs mentioned:

let the chocolate cool before adding it to the egg/cream mix - should be about the warmth of a babys bottle.

Do not overmix the chocolate into the egg/cream mix - this tart is sinfully heavy, and producing airbubbles will detract from this.

Cook for a longer time if you want a firmer (more brownie like) middle, and shorter if you want it runnier (more like fudge)

Add macadamias into the chocolate mix (around a handful) for a crunchy bite.

Try using gingernut biscuits...mmmmmmmmmmm

You could also use white chocolate for the filling!

We had leftover filling which we poured into mini muffin cases (and added macadamias). Unfortunately, these did not come out of the tin well (not greased enough?) but we ate them with a spoon anyway.

If you have leftover, you could try lining small tins with baking paper to ensure the mix doesnt stick to the side.